FM systems for hearing aid users

FM systems and modern radio transmission equipment can significantly improve speech intelligibility for hearing aid users, especially in acoustically challenging environments. Wireless technology transmits speech directly from the speaker to the hearing aid, bypassing distracting background noise, long distances, and reverberation. From school to work to leisure activities, these systems open up new possibilities for clear communication. The choice between analog FM and digital DM technology, as well as the right connection to the hearing system, are key aspects here.

Basic principle and technical definition

FM systems, also known as radio transmission systems, are hearing assistance technologies for the wireless transmission of audio signals using radio waves. They are an important addition to hearing aids or cochlear implants and serve the purpose of ensuring clear communication in acoustically challenging environments. The basic principle is based on transmitting the speech signal directly from the speaker to the listener, thereby circumventing the acoustic problems of the room.

The term FM system has evolved over time and derives from frequency modulation, which was used in older analog systems. However, modern systems are increasingly using digital transmission methods. The aim of all systems is to create the impression that the speaker is standing right next to the user. This can significantly improve the quality of life for people with hearing loss and enable them to participate more actively in social life.

Acoustic challenges in difficult listening environments

Despite advanced hearing aids, speech comprehension remains problematic in certain environments for people with hearing loss. The biggest challenges are background noise, distance from the speaker, and reverberation in the room. Hearing aids tend to amplify not only speech but also ambient noise, resulting in an unfavorable signal-to-noise ratio. This describes the relationship between the desired speech signal and the disturbing background noise.

As distance increases, the voice loses intensity while the noise level remains constant. This makes understanding even more difficult and leads to increased listener fatigue. In rooms with poor acoustics, reverberation further exacerbates the problem, as reflected sound waves interfere with direct speech transmission. FM systems can minimize or eliminate these disruptive factors by transmitting the voice clearly and directly to the hearing aid. The technology completely compensates for the attenuation of the voice over longer distances.

Structure and function of wireless transmission

A radio transmission system basically consists of two main elements: a transmitter with an integrated microphone and one or more receivers. The microphone picks up the speaker's voice signals, which the transmitter then converts into modulated radio signals and transmits. The receiver, which is worn by the hearing aid user, picks up the radio signal and converts it back into an analog audio signal that is fed directly into the hearing aid.

The speaker usually holds the microphone close to their mouth, either clipped to their clothing or in their hand. This proximity to the mouth is crucial for the quality of the transmission, as it ensures that the voice is recorded at the optimum volume while ambient noise remains significantly quieter. Ideally, the distance between the mouth and the microphone should not exceed 15 to 20 centimeters in order to achieve the best results.

Analog versus digital transmission technology

The original term FM system derives from frequency modulation, which was used in older analog radio systems. With this technology, the carrier frequency is modulated according to the audio signal. Modern systems increasingly use digital modulation (DM), often in the 2.4 GHz or DECT frequency range. These digital systems generally offer clearer sound quality and are better at avoiding interference that can occur with analog FM signals.

An important technical aspect is latency, i.e., the delay between the spoken word and its reproduction in the hearing aid. Analog systems have virtually no latency, while digital systems may have a minimal delay due to the nature of the system. However, this is typically in the range of a few milliseconds and is not perceived as disturbing by most users. In most cases, the advantages of digital technology in terms of sound quality and interference immunity outweigh the disadvantages.

Improvement of the signal-to-noise ratio in the far field

The decisive advantage of wireless radio transmission is the dramatic improvement in the signal-to-noise ratio, especially in the so-called far field, i.e., at a great distance from the speaker. Direct transmission of speech and reduction of ambient noise results in a dynamic gain of between 15 and 25 dB compared to the use of hearing aids alone. This improvement can make the difference between understanding and not understanding.

The systems enable users to understand speech better, even when the speaker is far away, sometimes at distances of up to 30 meters or more. This is particularly important in large rooms such as lecture halls, conference rooms, or theaters. The technology ensures that the speaker's voice always arrives at the same volume and clarity, regardless of their position in the room.

Compatibility and connection to hearing aids

Wireless systems can be connected to almost all standard hearing aids and cochlear implants, provided they have a suitable interface. The audio signal is transmitted to the hearing aid in various ways. The classic method is direct connection via an audio shoe with a Euro jack on the hearing aid. This is attached to the lower part of the behind-the-ear device and establishes a mechanical and electrical connection to the receiver.

Another proven option is wireless transmission via an induction loop worn around the neck, also known as a neck loop. This requires an activated T-coil (telephone coil) in the hearing aid. The induction loop generates an electromagnetic field that is received by the T-coil and converted into an audio signal. This method has the advantage that no direct mechanical connection to the hearing aid is necessary.

Modern Bluetooth integration

Modern hearing aids with Bluetooth technology can often receive the radio signal either via an intermediate accessory device or directly. These streamers act as a bridge between the FM transmitter and the Bluetooth-enabled hearing system. The advantage of this solution lies in the wireless connection and the often simpler handling. Some manufacturers offer integrated solutions in which the FM receiver is built directly into the hearing aid accessory.

Compatibility between different manufacturers can vary, which is why expert advice on assistive devices and technology is important. Hearing care professionals can check which connection option is best suited to the existing hearing system and make the necessary adjustments. The initial configuration is crucial for optimal functionality and should not be carried out without expert knowledge.

Microphone variety for different communication situations

There are different designs of transmitter microphones, each optimized for different situations. Lavalier microphones, also known as clip-on microphones, are ideal for personal 1:1 communication. They are ideally attached to clothing at chest height, about 15 to 20 centimeters from the mouth. This position ensures clear voice pickup with low susceptibility to background noise.

Table microphones or omnidirectional microphones are designed for meetings or small groups. They pick up voices from all directions around the table, enabling participation in group discussions. Handheld microphones can be passed around in larger groups, which promotes speaking discipline and ensures speech intelligibility for the user. With digital systems, multiple microphones can often be connected to each other in a network.

MultiTalker function for complex situations

This network capability enables access to different speakers in large meetings or classrooms. Modern systems such as Phonak's Roger technology allow multiple microphones to be active simultaneously and the receiver to switch intelligently between speakers. This is particularly valuable in classroom situations where both the teacher and individual students can speak.

Head microphones, which are worn on the head with a headband, offer a constant position relative to the mouth and are particularly suitable for teachers or lecturers who move around a lot. Choosing the right type of microphone depends on the specific application and should be done carefully to achieve optimal results.

Application in pediatric audiology and in school settings

FM systems are an indispensable aid for students with hearing loss. Classrooms often have high noise levels averaging 60 dB, while values of 35 dB or less are recommended for optimal speech comprehension. In addition, the room acoustics in many school buildings are problematic, with strong reverberation and poor sound insulation. Under these conditions, speech comprehension can be significantly impaired even with well-fitted hearing aids.

With the help of a radio system, children can hear up to 42 percent more speech in class. The teacher's voice always sounds the same volume, regardless of where they are in the classroom. This significantly reduces listening effort and allows students to concentrate better on the learning content. The use of such systems is generally beneficial for children and young people with severe hearing loss, but can also offer significant advantages for those with milder hearing loss.

Cost coverage and legal basis

In Germany, FM systems for children and adolescents can be obtained through the statutory health insurance's medical aids guideline. The costs are usually covered if the need is certified by a doctor and confirmed by a pediatric audiologist. Close cooperation between the school, parents, hearing care professional, and health insurance company is often necessary to provide the necessary care.

The systems are essential for meeting the need for improved speech and hearing development and reducing fatigue caused by listening effort. Kindergartens and preschools can also benefit from the technology, especially for children with severely impaired speech comprehension in noisy environments.

Use in auditory processing disorders

FM systems are also very useful for children and young people without conventional hearing loss if they suffer from auditory processing and perception disorders (APD) or attention disorders such as ADHD or autism spectrum disorders. People with APD have difficulty separating useful signals from background noise, even though their peripheral hearing is intact. The central processing of acoustic information in the brain is impaired.

The FM system provides clear and direct access to the speaker's voice by significantly amplifying the signal above the background noise. This can greatly improve speech intelligibility and attention. For this target group, there are special receivers that are worn directly behind the ear and do not require hearing aids. These so-called behind-the-ear receivers are connected to headphones and can be worn discreetly under the hair.

The provision of FM systems for AVWS often requires a pediatric audiological diagnosis and may be covered by health insurance in cases of severely impaired speech comprehension in noisy environments. However, the decision is made on a case-by-case basis and requires careful documentation of the hearing problems and their impact on school performance.

Areas of application in adult life

FM systems support adults in a variety of professional situations. During meetings, conferences, or presentations, they reduce background noise and amplify speech. Especially in open-plan offices or at events with many participants, this technology can make the difference between active understanding and frustrating guesswork. This makes it much easier to participate in professional life despite hearing loss.

In private life, FM systems improve communication in acoustically challenging situations such as noisy restaurants, family celebrations, or church services. The systems can also be used at concerts, theater performances, or cultural events if the organizer provides the appropriate transmission equipment. Mobile transmitters can also be connected to external audio sources such as televisions, computers, or telephones to stream sound directly to the hearing system in optimal quality.

Connection with media devices

For watching television at home, many manufacturers offer special TV adapters that are connected between the television and the FM transmitter. The sound is then transmitted wirelessly to the hearing aid without disturbing other people in the room. The volume can be adjusted individually while the television is playing at a normal room volume. This can prevent conflicts in relationships and make watching television together enjoyable again.

FM systems can also be helpful for phone calls. By connecting a phone adapter, the conversation is transmitted directly to both hearing aids, which increases intelligibility and allows for hands-free calling. Modern smartphones with Bluetooth can often be connected directly to appropriately equipped hearing aids, eliminating the need for additional adapters.

Stationary and mobile system solutions

Wireless transmission systems are available in two basic designs. Stationary systems are designed for fixed, larger spaces such as conference rooms, theaters, lecture halls, or classrooms. They have a permanently installed transmitter to which multiple audio sources can be connected. The range is designed for larger events and can be up to 100 meters or more, depending on the system and frequency range.

Mobile, handy devices are intended for personal use. They can be easily taken to different locations and serve as personal aids. The devices are compact, lightweight, and often fit in a jacket pocket. They are suitable for spontaneous situations such as doctor's visits, lectures, guided tours, or excursions. The range of mobile systems is typically 15 to 30 meters, which is sufficient for most everyday situations.

Soundfield systems as a collective solution

Soundfield systems are a special type of transmission system and are primarily used to improve general room acoustics. They consist of a wireless microphone for the speaker and one or more loudspeakers installed in the room. The voice is slightly amplified and distributed evenly throughout the room. Unlike FM systems, the sound is not reproduced in individual hearing aids, but via room loudspeakers.

This system benefits everyone present, including people with normal hearing, those with attention disorders, and non-native speakers. In classrooms, a soundfield system can improve the learning environment for all students and reduce listener fatigue. Teachers do not have to strain their voices as much, which also benefits their vocal health in the long term. However, a soundfield system does not replace the benefits of an individual FM system for children with hearing loss.

Practical handling and maintenance

After an initial adjustment period, the daily use of FM systems is usually straightforward. The transmitter must be connected to the supplied charger regularly after use. Modern devices have lithium-ion batteries that cannot be overcharged. The charging time is typically two to three hours, and the operating time is between eight and twelve hours, depending on the model.

The receiver is either powered directly by the hearing aid or draws its energy from the hearing system's batteries or rechargeable batteries. This significantly increases the hearing aid's power consumption. When using an FM system, it is therefore important to ensure that the rechargeable batteries are sufficiently charged or that fresh batteries are used. Some systems have their own rechargeable battery in the receiver, which must be charged separately.

Optimal microphone position and error prevention

The speaker should ensure that the microphone is not covered by clothing such as scarves, ties, or necklaces, as this causes annoying friction noises. For clip-on microphones, the ideal position is on the outside of the clothing. The microphone should point upwards towards the mouth and not be covered by hair or scarves. If you have long hair, it may be helpful to tie it back or position the microphone in a less hairy area.

In the event of a malfunction such as no sound, noise, or dropouts, systematic troubleshooting should be carried out. First, check the rechargeable or regular batteries in the transmitter and receiver. Then check that all plugs and connections are in the correct position. In systems with multiple channels, interference with other radio systems may occur. In this case, a different channel should be selected. The operating instructions usually contain a detailed troubleshooting checklist.

Interception security and social aspects

Unlike infrared systems, radio waves are not restricted by walls, so there is a theoretical risk that third parties outside the room could listen in. Modern digital systems often counter this risk with encryption methods. With analog FM systems, transmission is generally unencrypted, which should be taken into account in sensitive areas such as doctor's appointments or legal consultations. In such situations, digital systems with encryption may be the better choice.

Another, more social aspect is the fact that the use of external receivers clearly identifies people with hearing loss as such. In practice, this can lead to adults in particular being reluctant to use or request these devices in professional or academic environments because they want to avoid stigmatization. Modern, compact designs and integration into Bluetooth headsets can help to lower this barrier.

Acceptance and education

The acceptance of FM systems depends heavily on education and support in the social environment. In schools, it is important that teachers and classmates are informed about the technology and understand its benefits. If the teacher forgets to turn on the microphone or accidentally leaves it on when going to the bathroom, this can lead to uncomfortable situations. Good training for all involved is therefore essential.

In professional life, it can be helpful to inform colleagues and supervisors about the necessity and functionality of the technology. This promotes understanding and facilitates integration in discussions and meetings. Open communication about one's own hearing situation can break down barriers and improve collaboration.

Cost aspects and financing

The cost of FM systems can vary considerably depending on the model and manufacturer. Simple mobile systems start at around €1,500, while high-quality digital systems with multiple microphones and receivers can cost €3,000 or more. Stationary systems for larger rooms can be even more expensive. For children and young people, the cost is usually covered by statutory health insurance if the medical necessity is proven.

For adults, it is more difficult to have the costs covered. While hearing aids are covered by health insurance as standard, FM systems are often considered additional equipment. Cost coverage for adults is possible, but usually requires a detailed justification of the necessity, for example, for the pursuit of a profession or participation in educational measures. Under certain conditions, the integration offices or the Federal Employment Agency may also be considered as cost bearers.

Future prospects for transmission technology

Future developments aim to further improve audio accessibility and promote inclusion. A promising new technology enables a single radio transmitter to serve multiple receivers of different types simultaneously. The advantage lies in universal compatibility: the signal can be received by suitable hearing aids and cochlear implants as well as by normal Bluetooth headphones.

This would greatly increase accessibility in public event venues. Theatergoers, concertgoers, or conference attendees could access the broadcast on their own devices as needed. People with hearing loss would receive the same audio quality as everyone else without having to rely on special rental equipment. Integrating such systems into public buildings, cultural institutions, and educational facilities could be an important step toward greater participation.

Integration with smart home and assistance systems

The increasing connectivity of everyday devices opens up further possibilities. In the future, FM systems could be seamlessly connected to smart home systems. Doorbells, smoke detectors, or phone calls could be signaled directly through the hearing aid. Combining this with voice assistants could simplify operation and create new applications. Connecting modern televisions and hearing aids is also becoming increasingly convenient and versatile.

The miniaturization of technology is advancing, making receivers smaller and less noticeable. Future generations of hearing aids may have FM receivers already integrated, without the need for additional components. This would simplify handling and increase acceptance. The development toward universal, standardized transmission protocols could also improve compatibility between different manufacturers and make it easier for users to choose.